1. Field of the Invention
The present invention relates to a turbine blade that is exposed to a relatively high temperature atmosphere and a relatively low temperature atmosphere, for example, a turbine blade for use in a gas turbine and the like.
2. Background Art
Turbine blades for use in a gas turbine and the like, for example, include: a concave-curve-like pressure surface that is concaved along a flow direction of fluid; and a convex-curve-like suction surface that is convexed along the flow direction of the fluid. In such turbine blades, a phenomenon in which a laminar boundary layer of fluid formed on the suction surface is separated, that is, a laminar separation is conventionally known to occur. The laminar separation leads to noise or a decrease in the turbine efficiency. Therefore, in the example in Patent Document 1, there is proposed a technique of providing projections on the suction surface to positively form turbulence with which an occurrence of a laminar separation is suppressed.    Patent Document 1: Japanese Unexamined Utility Model Publication, First Publication No. H07-35702
For example, in a turbine in a jet engine of an aircraft, turbine blades are exposed to different temperature environments between when the aircraft is cruising and when it is taking off and landing. For example, when the aircraft is cruising, the turbine blades are exposed to a relatively low temperature environment (low temperature atmosphere) because the combustion energy of the combustion chamber provided at the previous stage of the turbine is low, that is, an engine output is low. On the other hand, when the aircraft is taking off and landing, the turbine blades are exposed to a comparatively high temperature environment (high temperature atmosphere) because the combustion energy of the combustion chamber is high, that is, an engine output is high.
In the turbine blades that are exposed to a low temperature environment in cruising and to a high temperature atmosphere in taking off and landing, there arises a phenomenon in which a laminar separation occurs in the low temperature atmosphere in cruising, while a laminar separation does not occur in the high temperature atmosphere in taking off and landing. This phenomenon is conceivably due to the fact that in a low temperature atmosphere in cruising, a laminar separation is likely to occur because of low Reynolds numbers while in a high temperature atmosphere in taking off and landing, a laminar separation is not likely to occur because of high Reynolds numbers.
Therefore, in the case where projections are provided on the suction surface as in Patent Document 1, a pressure loss of the turbine blade increases more than in the case without the projections, in a state of being exposed to the high temperature atmosphere in taking off and landing, that is, in a state where a laminar separation has not occurred. Consequently, there is a possibility of a decrease in turbine efficiency in spite of expectations.